It is well known that solid particles, such as proppants and gravels, must be transported during oil field production. In the case of proppants, the proppants may be delivered to a hydrocarbon recovery zone to prop open fractures in the formation to facilitate recovery of hydrocarbons. Horizontal wells drilled and completed in unconsolidated sand reservoirs have become feasible recently, due to new technology and completion methods. Wells of this type require sand control, for example such as long open hole gravel packs or the installation of mechanical sand exclusion devices (slotted liners, prepacked screens, etc.). Successful wells have been completed with horizontal, producing intervals as long as 4,000 ft. (1,220 m) using these methods of sand control.
Usually the wells are drilled with conventional drilling muds to the top of the pay zone and casing is set. The cement is then drilled out to the casing shoe and the shoe is tested. The drilling mud is then displaced with a "low damage potential drilling fluid" generally consisting of polymers, viscosity enhancers and particles for building a filter cake. The particles are usually graded salt (NaCl) or graded calcium carbonate (CaCO.sub.3). These compounds are used because they are soluble in undersaturated brines or hydrochloric acid.
After the open hole interval has been drilled to total depth, the gravel pack screen or sand exclusion device is placed in the open hole interval. To do this it becomes necessary to circulate the drilling fluid from the open hole so that the well can be gravel packed or the sand exclusion setting can be tested. Displacement of the drilling fluid with a solids-containing completion brine may be necessary. Concern about the physical erosion of the filter cake with the completion fluid is also always an issue. That is, the completion brine should not damage the filter cake to permit the completion or other operation to take place and protect the well bore during the entire operation.
Polymers have been used in the past as viscosifiers in completion fluids to carry or suspend solid particles in the brine. However, such polymers require separate breaker compositions to be injected to reduce the viscosity. Further, such polymers tend to leave a coating on the proppant even after being broken, which coating may interfere with the functioning of the proppant. Studies have shown that "fish-eyes" and/or "microgels" present in some polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and causing formation damage.
Further, because such completion fluids contain solid particles, there is concern that the solids will damage the existing rig pumps at the drilling site. Thus, separate pumps must be brought in and employed to pump the completion fluid down hole. Fracturing treatments using solids-free viscoelastic surfactant fluids are known, however, proppants would have to be delivered in a separate procedure. Viscoelastic surfactant-based gelled gravel carrier fluids are also known.
It would be desirable if a composition and method could be devised to overcome some of the problems in the conventional injection of solids-carrying completion fluids.